INTERPRETING GRAPHS AND DIAGRAMS

(NB All the figures and outcomes are made up.)

Question 1

The graph shows a L'Abbe plot of three placebo controlled studies of SSRls forsocial phobia

1. What is the NNT for study A?2. Which study is likely to have yielded the most precise estimate

of the treatment effect?

3. What is the significance of the fact that the circle for study Ccrosses the diagonal line?

100

EER (%) 9080

706050

4030

20

10

10 20 30 40 50 60 70 80 90100

CER(%)

QUESTION 2

The diagram shows a Forest plot of a meta-analysis of 5 RCTs of InterpersonalTherapy (IPT) for depression

weighstandardised mean

(%)difference (C.L)

Study A

--271.0 (0.75,1.25)Study B

~21-0.25 (-0.5, 0.25)Study C

-fa-210.25 (-0.25, 0.5)Study D

•151.5 (0.75,2.0)Study E

~15-0.5 (-0.75,0.25)

~ummary

•0.75 (0.65,0.85)(fixed effect)~ummary

:.:(random effect)0.5(-0.25, 1.5):

I I I I I I I I I I I I I I I I I-2 -1 0 1 2

Test for heterogeneity

X' =5.19;df = 4; P = 0.093

1. What does the tenn 'standardised mean difference' actually bloody meanactuall y?

2. Where is the line of equivalence in the diagram?

3. Regarding study A; taking the point estimate of effect size what proportion ofsubjects receiving IPT improved more than the mean of the control group?

4. Why are the blobs for individual studies of different sizes?

5. Define clinical, methodological and statistical heterogeneity.

6. Is there significant heterogeneity between studies in this analysis? (Give threereasons for your answer)

7. How would you interpret the two summary measures of effect?

8. Do you think that this meta-analysis was worth doing?

QUESTION 3

The diagram shows a Kaplan Meier Curve plotting time to first relapse for a sampleof 20 patients with schizophrenia following discharge from hospital.

1.00.90.80.70.60.50.40.30.20.1

30 60 90 120 150 180 210 240 '270 300330 360 390 I Time (days) I

1. Do you think the investigators found it difficult to arrange to dischargeeveryone on the same day?

2. What do the points at either end of the short horizontal lines represent?

3. What do the short vertical lines interrupting the horizontal lines represent.What assumption is made? What would be the effect of this assumption beingwrong?

4. What is the median survival time to relapse?

5. Sketch roughly on the diagram where the confidence intervals would be forthe curve as a whole

6. If a patient survived without relapse for 100 days, what would be theprobability of their surviving a further 100 days? (as in all the best exams youonly get full marks if you show your working)

QUESTION 4

From: 'A randomized controlled study of divalproex vs lithium vs placebo in themaintenance phase of the treatment of bipolar disorder.'

Subjects were patients with a hx of BAD presenting with mania not more than 3 monthspreviously and recovered to the extent that informed consent to decisions about prophylactictreatment was an option. After open label treatment for three months all medication waswithdrawn and they were randomised in a double blind fashion to maintenance tx in one ofthe three arms (Lithium, Divalproex or placebo) with the possibility of adjunctiveantipsychotic or benzodiazepine available as necessary.

Results for the endpoint 'any mood episode' are as charted below.

Any Mood Episode

-- Placebo

.............. Divalproex

- - - Lithium

0.8 ~

0.7'

0.6­

0.5~

0.4­

0.3"

0.2­

0.1 -

0.0 -~--'----"--'----'c---r--------r-""---"--

III1- __

L· L :

" ' ' , , :- - - ~ " "

4 8 12 16 20 24 28 32 36 40 44 48

Time in weeks to any affective episode: Kaplan-Meier survival curves (placebo, n =92; divalproex, n=187; lithium, n=90). Wilcoxon x2 = 0.95, P =.33 for divalproex vsplacebo; Wilcoxon x2 =1.03, P=.31 for lithium vs placebo; and Wilcoxon l = 3.54,P=.05 for divalproex vs lithium.

1. What are the median survival times for the three groups?2. Compare your answer to question 1 to the statistical analysis given in the

legend. Explain any apparent discrepancy3. What is the major omission ofthe diagram?4. Assuming that the randomisation procedure was adequate and all groups were

equal at baseline, give five possible reasons why the apparent result may bebiased